When retrying a failed BIO_RW_BARRIER request, we need tokeep the reference in ->nr_pending over the whole retry.Currently, we only hold the reference if the failed request isthe *last* one to finish - which is silly, because it would normally be the first to finish.

So move the rdev_dec_pending call up into the didn't-fail branch.As the rdev isn't used in the later code, calling rdev_dec_pendingearlier doesn't hurt.